🧠 You don't just inherit general intelligence – ability in math and language is also more than half determined by genes

• There has long been strong evidence that general intelligence is heritable. Now a large meta-analysis shows the same applies to specific abilities like math and language.
• The study draws on nearly 750,000 twin comparisons and shows that specific cognitive abilities are on average 56 percent heritable.
• The findings open up the possibility of using genetic profiles to tailor education to each child's cognitive strengths and weaknesses, before problems even have a chance to develop.

There has long been substantial evidence that general intelligence, known as g, both exists and is heritable. Someone who is above average in verbal ability is more likely to also be above average in math, memory and spatial reasoning. And genes are a large part of the explanation.

Yet this has been denied in wide circles, in journalism, teacher training and among cultural elites. Now a large new meta-analysis takes the findings a step further: not only is general intelligence heritable, but specific cognitive abilities are as well, each in their own right.

An analysis of nearly 750,000 twin pairs

A research team from King's College London and other institutions compiled data from 77 studies with a total of 747,567 twin comparisons. They investigated what proportion of variation in specific cognitive abilities is due to inheritance.

The study used the Cattell-Horn-Carroll model (CHC), a well-established framework for the structure of intelligence. At the middle level of the model sit 16 broader abilities, such as fluid reasoning, processing speed and quantitative knowledge. These abilities, called specific cognitive abilities (SCA), are the focus of the study. The researchers had twin data available for 11 of the 16 categories.

As heritable as general intelligence

The average heritability estimate for specific cognitive abilities came in at 56 percent, on par with the heritability of general intelligence at around 50 percent. Many had previously assumed that specific abilities were more shaped by environment and experience than by inheritance.

Heritability varied considerably across the different abilities. Quantitative knowledge and processing speed had the highest values at 64 percent. Reading and writing ability came in at 61 percent. At the lower end, short-term memory scored 41 percent, fluid reasoning 40 percent and auditory processing 39 percent.

The grouping of acquired knowledge, which includes reading, writing, math and subject knowledge, proved to be the most heritable category overall, with an average of 58 percent. Fluid reasoning, long considered to be most closely tied to general intelligence, had a comparatively low heritability estimate of 40 percent.

Heritable even independent of general intelligence

The most unexpected finding concerned what happens when general intelligence is removed from the specific abilities. The question was how much of the heritability of, say, mathematical ability merely reflects the inheritance of general intelligence, and how much is unique to math itself.

The results showed that specific cognitive abilities, corrected for general intelligence, were still 53 percent heritable on average. This despite the fact that a quarter of the variance in the abilities disappeared when general intelligence was removed.

In a sub-study on mathematical ability, heritability was 48 percent. When both general intelligence and reading ability were accounted for, the figure rose to 51 percent. For spatial ability, heritability was 39 percent for the ability itself and 27 percent when general intelligence was removed.

School-related abilities showed stable heritability

Reading, writing, math and general knowledge, abilities actively practiced in school, showed high and stable heritability values of around 60 percent throughout the school years.

Specific cognitive abilities did not follow the same developmental pattern as general intelligence. For g, heritability is known to increase with age, from around 20 percent in infancy to 60 percent in adulthood. For specific abilities the picture was different: heritability increased from 37 percent in early childhood to 60 percent in middle childhood, before declining to 46 percent in adulthood and 41 percent in later life.

Can be used to help children

The researchers highlight several concrete applications of the findings. Using what are called polygenic scores, a measure that combines the influence of thousands of DNA variants, it could become possible to predict a person's profile of cognitive strengths and weaknesses from birth. The researchers specifically mention the possibility of predicting aptitude for science and technology subjects independent of general intelligence.

Such genetic profiles could, according to the researchers, be used to strengthen children's cognitive strengths and minimize their weaknesses. Rather than waiting for problems to emerge, interventions could be put in place at an earlier stage.

The finding also challenges a common assumption in research, that the heritability of specific abilities mostly just reflects the heritability of general intelligence. The results open up a new field of research into the genetic foundations of specific cognitive abilities, separate from g.

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